In 3 patients, 2 men aged 62 and 43 years, respectively, and 1 woman aged 53 years, the medication prescribed to reduce blood pressure was insufficiently effective. Drug adherence was questioned. The first patient was afraid of the side effects mentioned in the medication information leaflet. The second patient had insufficient plasma levels of the medication but would not discuss the subject. The blood pressure of the third patient was uncontrolled despite treatment with three antihypertensive drugs. During a short hospital stay, her blood pressure responded favourably to treatment with only one of the three drugs. Subsequent repeated instruction did not improve her situation. Drug adherence is an important issue in daily clinical practice. In patients with asymptomatic conditions like hypertension, adherence is expected to be poor and worsen over time. Adherence is very difficult to measure. Risk factors for poor adherence include complex medication schedules, multiple dosing times, depression and real or suspected side effects. Measures to improve drug adherence include simplifying the medication schedule, discussing the schedule during check-ups, using automated blood pressure measuring devices at home, maintaining e-mail contact with the patient and involving a specialised nurse. Increased awareness of poor adherence is an important step toward improving hypertension treatment.